Existing methods and means for measuring twist in yarn, for the most part, rely on the measurement of the twist angle alone and take no account of the important fact that the twist being measured is dependent upon the ever-varying yarn diameter. Such methods include a ply-twist method of measurement wherein a sample of yarn is untwisted in order to determine the twist that has been imparted to the yarn. Another method provides an untwist-twist technique wherein the yarn extends while being untwisted and contracts while being twisted in the opposite sense of its original twist so that when the original length of the yarn is attained during twisting in the opposite sense the total number of revolutions from untwist to twist is deemed to be twice the total twist of the length of yarn under test. Another method as shown in G.B. No. 1,266,450 proposes measurement of twist as the yarn is being formed at a point upstream of the twist spindle while the yarn is rotating.
The existing devices and methods use one of the following techniques:
(1) obtain a measurement of twist from two measured quantities--twist-angle and the yarn "diameter";
(2) obtain a measure of twist as the ratio of the specimen's tendency-to-rotate to the yarn speed necessitating the specimen to be actually in the process of twist insertion;
(3) use the twist-angle as a measure of the yarn twist ignoring the variation in the yarn "diameter".